Fermentation processes are used for the production of food ingredients, feed ingredients, biofuels, such as ethanol, and other industrial chemicals. Fermentation processes require a supply of fermentable compounds. Presently, fermentable compounds are derived almost solely from starch crops and sugarcane. Such sources are of limited supply and of relatively high cost, limiting the ability to produce fermentation products at economically attractive prices, on the one hand, and increasing the prices of food, on the other.
Major effort has been expended in the development of fermentable compounds from alternative sources that are much more abundant and involve lower costs. Examples of such fermentable compounds are cellulosic compounds or lignocellulosic compounds, such as wood, agricultural residues, sugarcane bagasse, energy crops, residues from wood processing, etc., all of which are characterized in comprising polysaccharides, such as hemicellulose and cellulose. For effective fermentation, such polysaccharides ideally are hydrolyzed. Hydrolysis, particularly cellulose hydrolysis, requires relatively harsh conditions, such as the use of a high acid concentration and elevated temperatures. Under such harsh conditions, undesirable degradation occurs, in particular, of hydrolysis products such as hexoses and pentoses, but also of lignin, when present. Such degradation of hydrolysis products generates impurity degradation products, some of which are inhibitory to fermentation and thereby reducing the fermentation product yield. Such fermentation inhibitors include furfural, hydroxymethylfurfural and acetic acid.
While many methods have been proposed for the removal of such inhibitors from the fermentable compounds in order to minimize such inhibition, none are ideal. Treatments such as distillation, adsorption, addition of a base, overliming, contacting with an ion-exchanger and extracting with a solvent, for example, are all costly and present other difficulties as will be appreciated by the skilled artisan.
This invention provides, inter alia, relatively pure fermentable compounds, which are prepared by a process which removes fermentation inhibitors from solutions of fermentable compounds, and which method is cost-effective.